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Audi B6 S4 DIY S4 6MT Downpipe Removal

There are a couple of threads to assist in the Downpipe removal of the B6 S4. With their help i decided to post up a detailed DIY to guide anyone interested. Special thanks to Brandon (Bpitz15) for providing the pictures and information on the removal.

This DIY is for a 6MT. If you have the Tip version of the S4, you will need to drop the subframe for more room due to the beefier transmission.
Tools/Equipment required:

First thing you want to do is jack up the car and place four stands on the designated jack points. Raise the stands up as high as possible- You will need some room to work under the car. Your car should look similar to this...

2. Belly Pan Removal

Take your flat head screwdriver and remove the screws on the belly pan as shown below.

Once the belly pan is removed go ahead and remove the rear cover (3 screws).

3. Catback Exhaust Removal

Depending on your exhaust will dictate what tools you need to take the Catback off. The bolts that connect the downpipe/catback are 15mm. Use a deep socket to loosen and remove them.

The muffers are held on by rubber hangers. Each hander consists of two 13mm bolts. Unbolt the hangers and remove them with the mufflers. There are also two hangers located in the mid-section of the cat-back. Grab a flat head and lubricant to remove the rubber hangers from the mounts.

4. Remove Upper O2 Sensor Connectors

Its time to pop the hood and disconnect the connectors for the O2 sensors. Lets start on the passenger side. Locate the plug on the fire wall 2nd from the left as shown in the picture.

Once located, slide the connector out of the holder. Disconnect the plug (It will slide out with the downpipe later on).

Now on to the drivers side. Take your philips screw driver and remove the screw holding your coolant tank in place.

Once the screw is removed, pull the tank toward you to release it from the rear clips. Next, move your coolant tank to the side to expose the driver side plugs located on the fire wall.

The O2 sensor connector is located 2nd from the right, very similar to the passenger side one. Before you disconnect it, remove the silver fabric piece of heat shield around the wire. It has two snaps and is wrapped around about 4 different wires. Undo these snaps and remove fabric. Now disconnect the connector in the same manner as the passenger side.

5. Axle Shield Removal

Time to get under the car. You will notice there is very little room to get to the manifold/downpipe bolts. To free up some space we will take off the axle shields.

This can be very tedious. There are 3 allen bolts on each shield (6 total) that mount to the transmission. You should see something similar to this...

The bolts are located at 10 o'clock, 12, and 2. The general position is shown above with the red circles. The top most bolt can be a pain to get out as you will not be able to see it. You must go by feel.

Trust me there will be lots of cursing and frustration during this part. Once you remove the shield do the same on the opposite side. When they are off you will have much more room to work.

6. Pre-Cat O2 Sensor Removal

Before we go after the manifold bolts, remove the Pre-Cat O2 Sensors. Take your 7/8 wrench and remove both. IMPORTANT: Mark which O2 sensor goes in which DP. You don't want to put them back in the wrong place.

7. Manifold Bolts

Next step is to remove the manifold bolts. There are three on each side (13mm). The lower one on each side is the easiest to remove. Stubby ratchet and extension will work fine.

The other two might be a little more difficult to get to. There are several ways to go about this. You can continue to use the stubby ratchet, extension, and a swivel to get at the other two. I found it easier to attach a 2 foot extension and work the bolts out that way. Members have found either way to work.

8. Downpipe Transmission bolts

Last step is to unbolt the 16mm bolts (one on each downpipe) that hook up to the transmission. Once these are removed the downpipes are ready to come out.

9. Removal

Now that the downpipes are free you can start to slide them out. Its a little tight so you might have to do a little bit of twisting.

Done! You have successfully removed the DPs from your car.

Installation is pretty much the same steps in reverse. Make sure you guide your O2 sensors to the engine bay before you start attaching the new/reinstall downpipes.

If you are installing piggie pipes i recommend you use O2 spacers for the Pre-Cat sensors. You will most likely throw a CEL if this is not performed. There is sufficient room to use 2 spacers on each O2 sensor. Make sure you drill out the upper spacer (the one the 02 sensor is screwing into) so you are getting enough air flow.

Torque specs for the manifold bolts are 27 nm (Thanks to littleredwagen).

If you have any questions please feel free to post them here. I hope this help everyone.

Re: B6 S4 DIY: S4 6MT Downpipe Removal

I actually didnt. I was able to push the O2 sensor up toward the engine bay and grab it from the top. It might of been easier to do it your way. Do you think i should add that for reinstall?

do what you gotta do.

You tried it the hard way... i didnt even try to do it w/ out the strings so i wouldnt know how difficult it is to do it the way you said. If its manageable than there is no need to edit it. But if it could save someone 10-20 mins than throw it up.

Re: B6 S4 DIY: S4 6MT Downpipe Removal

Think I'm gonna tackle this tomorrow to try and find a leak.

My catback is welded to my downpipes, if I leave the hangers in the rubber mounts and just unbolt them it shouldnt be to much more of a pain right? I mean to get it all out in 1 peice?
I have accecss to a lift at work but I think think this job might need some beers so driveway and ramps it is

SomeGuyInAChair - "I'll be honest about why I signed up for a car forum without thorough knowledge of cars. I merely did a Google search with the following key words: "milf cougar forum advice help tips"

Re: B6 S4 DIY: S4 6MT Downpipe Removal

Originally Posted by ZachPDX

Think I'm gonna tackle this tomorrow to try and find a leak.

My catback is welded to my downpipes, if I leave the hangers in the rubber mounts and just unbolt them it shouldnt be to much more of a pain right? I mean to get it all out in 1 peice?
I have accecss to a lift at work but I think think this job might need some beers so driveway and ramps it is

i think it is easier that way. I have tried both methods and if you have an extra set of hands to hold the exhaust while you bolt it back up it goes quite easily.
Good luck!

Re: B6 S4 DIY: S4 6MT Downpipe Removal

If your talking about the muffler mounts then yes, i always take the hangers out with the mufflers. The mid-section hangers though must be removed from the rubber mounts, You cant disconnect the rubber mounts.

SomeGuyInAChair - "I'll be honest about why I signed up for a car forum without thorough knowledge of cars. I merely did a Google search with the following key words: "milf cougar forum advice help tips"

SomeGuyInAChair - "I'll be honest about why I signed up for a car forum without thorough knowledge of cars. I merely did a Google search with the following key words: "milf cougar forum advice help tips"

Re: B6 S4 DIY: S4 6MT Downpipe Removal

Thanks for the help yesterday joeycuccaro . I got the belt replaced no problem but even after getting the axel shields off I couldn't even get 1 of the downpipes nuts to budge .

Glad i could help. Yeah they can be a bit of a pain to get off especially if the car has higher miles. Trick is to soak them with PB blaster and let it sit for a little bit. Come back and repeat the process. After a few hours they should loosen up.

Re: B6 S4 DIY: S4 6MT Downpipe Removal

This writeup (thanks joey) combined with the info in your "how to avoid a CEL" thread and we can make piggie pipes. Awesome

What's the process? Remove the DPs, hollow out the precats, use two spacers for each precat O2 sensor, relocate the main cat O2 sensors to behind the main cats (and block of the stock main O2 sensor location) and then reinstall the DPs?

Also, did you reinstall your axle shields? I know most B5 S4 guys just left the shields off since they're such a PITA to remove/reinstall. With hollowed precats I think the shields might not be as important since without the cat doing it's job, the amount of heat put out in that area will be greatly reduced.